The impact of extratropical transition on downstream predictability

Sarah Jones, Doris Anwender, Christian Grams, Julia Keller, Simon Lang

Institut für Meteorologie und Klimaforschung, Karlsruhe Institute of Technology

Completed projects

Christian Grams: "Quantification of the downstream impact of extratropical transition for Typhoon Jangmi and other case studies"

Julia Keller: "Diagnosing the Downstream Impact of Extratropical Transition Using Ensemble Forecasts "

Simon Lang: "The structure of singular vectors associated with extratropical transition of tropical cyclones"

Doris Anwender: Data denial experiments for extratropical transition, Data impact studies using IASI satellite observations


A poleward moving tropical cyclone that interacts with the midlatitude flow and transforms into an extratropical system – i.e. undergoes extratropical transition (ET) – can cause a severe reduction in the forecast skill for the midlatitude flow downstream. In this project we will investigate the mechanisms that determine this interaction and the associated reduction of predictability. We will apply potential vorticity inversion to analyses, deterministic forecasts, and ensemble forecasts including TIGGE data. We will conduct idealised modelling experiments with the COSMO model and perform high resolution case studies with the COSMO model nested in ensemble members representative of a particular ET scenario. Using an empirical orthogonal function (EOF) and fuzzy cluster analysis we will analyse TIGGE data. Using the ECMWF ensemble prediction system we will carry out experiments to investigate the role of initial perturbations and stochastic physics in ensemble forecasts of ET. Finally, we will conduct data impact experiments to assess the importance of observations related to an ET event for the downstream predictability. This project will contribute to the planning of and analysis of the results from the T-PARC experiment


To quantify (i) the influence of tropical cyclones undergoing extratropical transition on the development of high impact weather in the midlatitudes and (ii) the role of midlatitude features in initiating tropical cyclogenesis; to investigate the representation of both of these aspects in ensemble forecasts, and to develop diagnostic techniques for analysing ensemble output. The results of this project will be used to develop the concept of a European-led regional campaign. During the first 3 year phase a combination of idealised modelling, analysis of TIGGE data, global ensemble experiments and data impact studies will be applied to extratropical transition cases. This study will contribute to the planning of the THORPEX Pacific Asian Regional Campaign and the analysis of the impact of lidar and dropsonde data from the DLR-Falcon as well as in-situ and remote sensing data from other platforms. The focus here will be on T-PARC cases related to the downstream impact of ET